EP0558739A1

EP0558739A1 - Method and device for producing thin films of liquid in the form of a coating or sheet.

Info

Publication number: EP0558739A1
Application number: EP92920892A
Authority: EP
Inventors: Thomas Berrenberg; Ingo Steinbach
Original assignee: Access eV; Glyco Metall Werke Glyco BV and Co KG
Current assignee: Access eV; Glyco Metall Werke Glyco BV and Co KG
Priority date: 1991-09-25
Filing date: 1992-09-23
Publication date: 1993-09-08
Anticipated expiration: 2012-09-23
Also published as: ATE152940T1; WO1993005906A1; DE4131849C1; EP0558739B1; DE59208496D1

Abstract

In order to produce improved films for application to a substrate without the need for additional devices for heating the substrate, the liquid is applied to the substrate in larger amounts than necessary for the formation of the coating. The excess liquid is drawn off and particularly re-used. The liquid is fed, by means of appropriate pressure control, on to the substrate in a laminar-flow stream at least in the contact zone between liquid and substrate. Described is a flow applicator (1) which, in addition, has a discharge channel (4) above the outlet channel (5). Between the input channel (2) and the discharge channel (4) is a channel (3) in the vicinity of which the excess liquid is used to heat the substrate (30).

Description

Method and device for producing thin layers of liquids as a coating or film

The invention relates to a process for the continuous production of thin layers of liquids as a coating or film, in which a substrate and a pouring point are moved relative to one another and in which during the movement the liquid is poured onto the substrate at the pouring point to form a liquid band, and that infused liquid band is allowed to solidify. The invention also relates to a flower which can be used in this method, the flower having a liquid supply channel and an outlet restriction part which, together with the substrate, forms an outlet channel.

From DE-PS 36 38 901 a method for the continuous casting of a metal strip or a metal strip is known, in which a pouring device is used which has a vertical feed channel which is delimited by side walls, the rear side wall to form an outlet channel opposite the front side wall is arranged offset upwards. The substrate is moved in a predetermined direction under the pouring device. A heating device is provided in front of the pouring device in order to heat the substrate to a temperature which is above the melting point of the metal to be applied.

The provision of an additional heating device for heating the substrate increases the cost of production thin layers. Depending on the material used and the desired temperature, the preheating of the substrate can also lead to destruction or deformation of the substrate.

Another disadvantage of the known device is that due to turbulence in the liquid, the applied layer can have a corrugated structure or at least different layer thicknesses.

The same problems also occur in the flower known from DE-OS 39 38 234, which has an outlet restriction part in the form of a plate delimiting the outlet channel. In addition, in the case of thicker layers, the material in the region of the flower could freeze due to the temperature difference from the substrate if the substrate is not preheated. This is particularly problematic when, as shown in DE-OS 39 38 234, part of the liquid is directed in front of the flower against the direction of movement of the substrate, because this causes the solidification front of the applied liquid band to migrate too far into the flow area and can completely block the flow of the flow.

The object of the invention is to provide a method and a flow with which an additional preheating device can be largely dispensed with and an improved design of the layer applied to the substrate, in particular with regard to the uniformity of the layer thickness is achieved.

This object is achieved with a method according to claim 1 and a flower according to claim 9

The method is characterized in that a larger amount of liquid is poured onto the substrate than is required for the formation of the thin layer, and that the excess amount of liquid is removed. A high volume flow is thus generated on the substrate, the amount of liquid which is not required for the formation of the thin layer being used to heat the substrate. Preferably, two to ten times the amount is poured onto the substrate, which is required for the formation of the liquid band and thus for the coating. The heating of a surface layer of the substrate can thus be controlled via the size of the excess amount, taking into account the heat capacities of the liquid and the substrate. In order to ensure sufficient heating of the substrate, the point at which the excess amount of liquid is removed is preferably arranged at a distance from the pouring point.

The fact that the preferably overheated liquid to be applied causes the heating of a surface layer of the substrate, in contrast to separate upstream heating devices, the substrate does not become entire Thickness is heated so that a cooling capacity remains in the substrate. The surface temperature rises continuously behind the pouring point and drops again after the excess flow has been separated off. The optimum temperature for the formation of the bond between layer and substrate is thus achieved in the area of the flow. This improved temperature control is not possible in the method according to the prior art, since the temperature between the heating device and the pouring point or between the pouring point and the outlet channel of the flow may have dropped below the desired temperature again due to the low volume flow. Another advantage is that the heating by means of the excessive volume flow results in a brief superficial heating of the substrate, so that damage and deformation of the substrate are largely avoided, which in turn also improves the quality of the coating. In particular, the method according to the invention improves the bond, for example between a metallic sliding layer and a steel substrate.

Furthermore, it has been found that when working with excess amounts of liquid, the quality of the coating, in particular with regard to the constancy of the layer thickness, is significantly improved. The improvement is particularly evident when the upper liquid layers of the liquid band facing away from the substrate are discharged as an excess amount of liquid. Behind the pouring point, the poured-on liquid flows in the direction of movement of the substrate on the substrate in the direction of the point where the excess amount of liquid is removed (discharge point). Due to the movement of the substrate, turbulence presumably only occurs in the upper liquid layers, which, however, cannot have a negative effect on the quality of the coating if these upper liquid layers are preferably removed.

According to a further embodiment, the excess amount of liquid is removed shortly before the solidification front of the liquid band, because this largely prevents the formation of new turbulence behind the discharge point.

A further improvement in the layer quality is achieved in that the poured-on liquid is conducted as a laminar flow between the pouring point and the discharge point, at least in the substrate / liquid contact area. For this purpose, an overpressure is set in the liquid at the pouring point and a negative pressure in relation to the environment at the discharge point. It is advantageous here if the negative pressure is set in such a way that a film-forming meniscus forms immediately behind the discharge point. In this case, the surface of the liquid band behind the discharge point is no longer in contact with components of the pouring device, which could possibly generate further turbulence in the liquid band and thus lead to a different formation of layer thicknesses. Since the materials for forming thin layers are often quite expensive, the excess liquid which is removed is preferably returned and, after heating, is fed back to the substrate, for example in the storage vessel.

In order to carry out this method, a flow device is provided which, in front of the outlet channel and at a distance from the feed channel, has a discharge channel for removing excess liquid. Between the feed channel and the discharge channel, the underside of the flow is designed together with the substrate to form a flow channel, which at least in sections has a larger cross section than the outlet channel, so that the turbulence which forms in the upper layers of the liquid can be drawn off from the discharge channel.

The discharge channel extends over the entire width of the flow and is arranged above the flow channel, preferably at an incline, so that the upper liquid layers can get into the discharge channel and be discharged without additional turbulence formation in the branching point flow channel / outlet channel / discharge channel.

The overpressure provided in the process in the area of the pouring point has the advantage that air pockets between the liquid and the substrate are avoided. However, it must be ensured that the liquid between Entry restriction part and substrate cannot exit against the substrate movement. The overpressure is set such that only an overpressure meniscus is formed under the entry restriction part.

In order to be able to set the pressure conditions provided according to the method in the area of the pouring point and in the area of the discharge point, the feed channel and the discharge channel are connected to suitable pressure devices. This can be a pump arranged outside the discharge channel, which generates the desired negative pressure in the region of the branch point in the flow. A pump can also be provided upstream of the feed channel, and a corresponding arrangement of a storage container above the flow can also ensure the desired pressure conditions.

Fine-tuning of the pressure conditions in the flow channel can be achieved by structuring the underside of the flow in the area of the flow channel behind the feed channel and in front of the discharge channel. The underside of the flow preferably has a flow resistance in the form of a bead running perpendicular to the direction of movement behind the feed channel and in front of the discharge channel. The first bead arranged behind the feed channel throttles the liquid flow, so that an overpressure is established at the pouring point. The pressure then decreases behind the first bead, the configuration of the second bead arranged in front of the discharge channel being selected such that at the Branching point, the desired negative pressure is present.

The discharge channel is preferably connected to the supply channel via a return channel, so that the skimmed-off amount of liquid can be used again.

A particularly simple embodiment of the flow is achieved if a core part is inserted in the interior between the inlet restriction part and the outlet restriction part, which delimits the feed channel, the flow channel and the discharge channel. When a return of the excess amount of liquid in Fl ^'to be made ießer, the upper side of the core part can accommodate the return duct or limit. The flow can also be open at the top, ie with a free liquid surface. The fluid flow is started by the moving substrate.

The entry restriction part / surface distances of the substrate (d ₁ ) and

Exit restriction part / surface of the substrate (d ₂ ) can be preset, or the flow can rest freely on the substrate, ie float on the liquid, so that d, and d _? adjust according to the flow conditions and the pressures. The flow can also be attached to a holding device, wherein it is rotatably mounted either at the front or at the rear end. The flower then takes no parallel position regarding the substrate. To optimize the flow, the flow can also be fastened in such a way that d _{2 is} variable.

Exemplary embodiments of the invention are explained in more detail below with reference to the drawings.

Show it:

FIG. 1: a longitudinal section through a flow with liquid and substrate,

FIG. 2: a partial longitudinal section through a flow according to FIG. 1 with a modified flow guide,

FIG. 3: a longitudinal section through a flow machine according to a further embodiment,

FIG. 4: a longitudinal section through a flow in accordance with a further embodiment,

Figure 5: The front view of a flow machine,

FIG. 6: the top view of a flow machine according to FIG. 1,

Figure 7: A representation of flow profiles in the flow channel and

Figure 8: The schematic representation of a flow with additional devices. In Figure 1, a flow 1 is shown in a schematic representation in longitudinal section, under which a ribbon-shaped substrate is moved in the direction of the arrow. The front of the flow 1 is formed by an entry restriction part 7, which is arranged inclined at an angle to the front and ends at a distance d above the substrate 30. A gap 18 is thus left free between the entry restriction part 7 and the surface of the substrate 30 (see also FIG. 5).

Between the inlet restriction part 7 and the front side 9 of a core part 8 arranged in the interior of the flow 1 there is the feed channel 2 through which the liquid to be applied to the substrate, e.g. a molten metal is fed from above. The feed channel 2 is also arranged inclined forward. As can be seen from the top view in FIG. 6, the feed channel 2 extends over the entire width of the flow 1 and is laterally delimited by the side walls 16 and 17.

The flow channel 3 is formed between the underside 10 of the core part 8 and the substrate 30 and continues at the branching point 33 in the discharge channel 4 and in the outlet channel 5. The outlet channel 5 is delimited by the outlet restriction part 6 and the substrate 30. The discharge channel 4 is located between the rear 11 of the core part 8 and the outlet restriction part 6 and thus above the Outlet channel 5. The discharge channel 4 also extends, as can be seen from FIG. 6, over the entire width of the flow tube 1 and is also laterally delimited by the side walls 16 and 17.

The liquid intended for the coating is applied through the feed channel 2 from above onto the substrate 30 (pouring point) and, among other things. deflected in the direction of the outlet channel by the moving substrate. A larger amount of liquid is supplied through the feed channel 2 than is necessary for the formation of the liquid band 36.

In the area of the gap 18, the surface of the liquid is exposed and care must be taken at this point that air pockets between the liquid and the substrate surface are avoided. Such air pockets are largely avoided if the liquid is guided with regard to the pressure in such a way that an overpressure meniscus 34 is formed. The pressure P ₁ and in particular the pressure P- are set such that they are above the ambient pressure, as a result of which the liquid for forming the overpressure meniscus 34 presses slightly into the gap 18. The pressure P, however, must not be set so high that the gap 18 is filled with liquid.

The supplied liquid then enters the flow channel 3 and from there into the discharge channel 4 or the outlet channel 5. The excess amount of liquid heats on the way from The feed channel 2 to the discharge channel 4 has the substrate 30 moved under the flower 1, so that the substrate 30 at the branching point 33 or in the region of the outlet channel 5 has the desired temperature for optimally binding the layer on the substrate. The cross section of the feed channel 2 and the cross section of the flow channel 3 are adapted to the amount of liquid required for heating the substrate 30 and are larger than the cross section of the outlet channel 5.

Since the liquid in the flow channel 3 is essentially guided through the surface of the substrate 30 and the underside of the core part 8, turbulence occurs which can lead to an impairment of the layer 31. It must therefore be ensured that there is no turbulence in the flow channel 3, at least in the liquid layers adjacent to the substrate 30, which then have an unfavorable effect in the outlet channel 5 when the liquid band is formed.

FIG. 7 shows three flow profiles in the flow channel 3, which are identified by I to III. The flow profile II corresponds to the shear flow when the material flow m = 1/2. q. v corresponds. Here q means the cross section of the flow channel 3 and v the flow velocity of the liquid in the flow channel 3. If the liquid flow is reduced, profile I is obtained. Here the maximum speed gradient is due to the Top of the substrate and can therefore cause turbulence formation, which is undesirable. However, if you increase the material flow, you get profile III. The maximum speed gradients are on the stationary core underside. Turbulence is therefore only to be expected in the area of the core underside, so that a laminar liquid flow leads to the outlet channel 5 at least in the contact area of the substrate 30. The turbulence which forms on the stationary core underside is discharged through the discharge duct 4 arranged above the outlet duct 5. This ensures that in the outlet channel. 5 a largely turbulence-free flow occurs, so that there are no differences in thickness in the liquid band 36 and thus in the solidified layer 31.

At the end of the outlet limiting part 6, the film-forming meniscus 35 forms, in front of which a negative pressure must be set in relation to the surroundings in order to achieve a film thickness x which is less than half the height d _{2 of} the outlet channel 5. The pressure P. must therefore be chosen lower than the pressure P. The negative pressure in the outlet channel 5 causes a backflow, whereby the film thickness x can be reduced with the same d. In addition, the position of the film-forming meniscus can either be at the end of the outlet limiting part 6 - as can be seen in FIG. 1 - or at the beginning of the

Exit restriction part 6 - as can be seen in Figure 2 - are forced. In the representations shown here, the solidification front 32 lies in the Area of film-forming meniscus 35.

An aluminum alloy (AlPblO) was applied to a substrate made of lead bronze, which was pre-ground, with the flower according to FIG. The speed of the substrate was 1 m / sec. The maximum tolerable temperature of lead bronze at the melting temperature of lead is approx. 325 ° C, while the homogenization temperature of the aluminum lead alloy is approx. 1200 ° C. The

Aluminum alloy was used in a lot of

40 cm 3 / sec. fed, of which 34 cm3 / sec. were removed again, so that with about seven times

Excess amount of liquid was worked. The

Surface layer of the lead bronze in the area of the

Fließers was heated to a temperature of approx. 600 ° C, so that an optimal bond between

Substrate and aluminum alloy was achieved.

With a flower according to the prior art, it is not possible to apply one

Liquid film of 200 Λim for the

Connection required temperature for

To achieve contact temperature because the

The heat capacity of the thin liquid layer is insufficient. The layer thickness was 0.2 mm, the

Fluctuations in the layer thickness were less than 10%.

Here, the pressure in the feed channel was approximately

P -. = 1.05 bar and in the area of the pouring point set to about P _c _> = 1.1 bar. In the area of

At branch point 33, the pressure of the liquid was approximately P = 1 bar and the pressure in the outlet channel was approximately P ₄ = 0.9 bar. The pressure in the upper area of discharge channel 4 was P_ = 0.8 bar.

The position of the film-forming meniscus 35 at the beginning of the outlet channel 5 (see FIG. 2) offers the advantage that it is located on the underside of the

Outlet restriction part 6 in the outlet channel 5 cannot form new turbulence, which can lead to instabilities of the film-forming meniscus 35 located at the end of the outlet restriction part 6. In the embodiment shown in FIG. 2, the film-forming meniscus 35 lies directly on the discharge channel 4.

The deflection of the upper layers of liquid, in which the turbulence is present, is facilitated in that the discharge channel 4 is arranged inclined towards the rear of the flow 1.

FIG. 3 shows a pressure-optimized variant of the flow 1, which is characterized, inter alia, in that the edges and transitions are rounded off, in particular in the area of the core part 8. A first bead 13 and a second bead 14 are formed on the underside of the core part 10 in order to further influence the pressure profile in the flow channel 3. The two beads 13 and 14 extend over the entire width of the flow channel 3. The first bead 13 leads to an increase in the pressure P ₅ and at the same time to a pressure decrease from P- to P ,. The formation of the bead 14 is responsible for the setting of the negative pressure P_ if P ₃ also denotes a negative pressure. As can be seen in FIG. 8, the feed channel 2 is connected via a feed line 42 to a storage container 40, which can be closed by means of the stopper 41, with which the discharge quantity can also be regulated. By selecting the height of the reservoir 40 above the flow 1, the pressure conditions in the feed channel 2 are set. The discharge channel 4 is connected to the reservoir 40 via a return line 43. To form the desired negative pressure in the discharge channel 4, a pump 44 is provided which simultaneously transports the excess amount into the storage container 40.

The excess liquid can also be returned in the flow, as shown in FIG. 4. In the embodiment shown here, the liquid flow is set in motion by the substrate 30 moved in the direction of the arrow. The pressure optimization is carried out exclusively by the cross-sectional design of channels 2, 3, 4 and 15. As can be seen in FIG. 4, the cross-sectional design is determined exclusively by the shape of the core part 8. In contrast to the embodiment according to FIG. 3, the core part 8 has on the underside 10 only a bead 14 in the area in front of the discharge duct 4. The first bead is omitted because no flow limiter is required due to the lack of a pressure device.

The return duct 15, which connects the discharge duct 4 and the feed duct 2 to one another, is formed by the Surface 12 of the core part 8 and the liquid level defined. The liquid running through the outlet channel 5 should preferably be replaced by adding new liquid in the return channel.

REFERENCE SIGN LIST

Flow feed channel flow channel discharge channel outlet channel from the access restriction part inlet restriction part core front underside back top top 1 bead 2 bead return channel 1 side wall side wall gap substrate solidified layer solidification front branching point overpressure meniscus film-forming meniscus liquid band reservoir plug plug feed line return line pump

Claims

PATENT CLAIMS

1. A process for the continuous production of thin layers of liquids as a coating or film, in which a substrate and a pouring point are moved relative to one another and in which during the movement the liquid is poured onto the substrate at the pouring point to form a liquid band and the poured liquid band solidified, characterized by

that a larger amount of liquid is poured onto the substrate than is required for the formation of the liquid band and that the excess amount of liquid is removed.

2. The method according to claim 1, characterized in that the upper liquid layers of the liquid band facing away from the substrate are discharged as an excess amount of liquid.

3. The method according to any one of claims 1 or 2, characterized in that the excess amount of liquid is removed at a discharge point behind the Auf¬ pouring point.

4. The method according to claim 3, characterized in that the infused Liquid is poured between the pouring point and discharge point at least in the substrate / liquid contact area as a laminar flow.

5. The method according to any one of claims 1 to 4, characterized in that an excess pressure is set in the liquid at the pouring point and a negative pressure in relation to the environment at the discharge point.

6. The method according to claim 5, characterized gekenn¬ characterized in that the negative pressure is set such that a film-forming meniscus forms immediately behind the discharge point.

7. The method according to any one of claims 1 to 6, characterized in that the two to ten times the amount of liquid required for the liquid band is supplied

8. The method according to any one of claims 1 to 7, characterized in that the amount of liquid removed is returned.

9. Flower for applying a liquid to a substrate to form a thin layer, the substrate and flower being movable relative to one another, with a liquid supply channel and with an outlet restriction part which, together with the substrate, forms an outlet channel, characterized in that that in front of the outlet channel (5) at a distance from the feed channel (2) a discharge channel (4) is provided for removing excess liquid, and

that between the feed channel (2) and the discharge channel (4) the underside (10) of the flow (1) is designed together with the substrate (30) to form a flow channel (3) which at least in sections has a larger cross section than the outlet channel (5 ).

10. Flower according to claim 9, characterized in that the discharge channel (4) adjoins the exit part (6).

11. Flower according to claim 9 or 10, characterized in that the underside (10) of the flower (1) is structured in the area between the feed channel (2) and discharge channel (4).

12. Flower according to claim 11, characterized in that the underside (10) behind the feed channel (2) and in front of the discharge channel (4) each has a flow resistance in the form of a bead extending perpendicular to the direction of movement (first bead 13, second bead 14) .

13. Flower according to one of claims 9 to 12, characterized in that the distance of the first bead (13) to the surface of the substrate (30) is less than the distance of the second bead (14) to the substrate surface.

14. Flower according to one of claims 9 to 13, characterized in that the discharge channel (4) extends over the entire width of the flower (1) and leads from the flow channel (3) upwards, so that in the flow channel (3) above ¬ lying liquid layers are removable.

15. Flower according to one of claims 9 to 14, characterized in that the feed channel (2) is connected to a pressure device for setting an excess pressure in the liquid in the region of the pouring point.

16. Flower according to one of claims 9 to 15, characterized in that the discharge channel (4) to a pressure device for setting a negative pressure in the liquid at the Ver¬ branching point (33) between the flow channel (3), outlet channel (5) and discharge channel (4) is connected.

17. Flower according to one of claims 9 to 16, characterized in that the discharge channel (4) via a return channel (15, 43) with the feed channel (2) is in communication.

18. Flower according to one of claims 9 to 17, characterized in that in the interior of the flower (1) a core part (8) is arranged, the feed channel (2), flow channel (3) and discharge channel (4) delimits.

19. Flower according to one of claims 9 to 18, characterized in that the core part (8) with its upper side (12) delimits the return channel (15).